If you want to avoid the busy E73, this is a good alternative. Mostly just scenic, but some parts are proper fun cornering.
Road surface is spotty, but takes 100-110kmh on BMWs... probably not a great idea with sportbikes.

This was a trip which ended up to be a little bit longer as originally planned. From Tuk there is about 20km gravel road through nice valleys and mostly forrest. If you end up in the Plitvitzer Lakes, calculate at least 3 hours for the visit. They have lockers there, so you can lock up your motorcycle gear and change into some easier clothing. The visit as such is awsome.